Chemical Engineering Chapter 24 But U will increase because the mass

24-15

24.15 (a) Pump and system curves:

46.1

hm50

hm73

hm 73 3

3

max

v

46% scale-up

Heat Exchanger:

lm

ss

TUAQ

mQ

20% scale-up

Vaporizer limits scale-up since Tmax for steam is 160 C.

(b) NPSHAPtank gh PfP*

24-16

24.16 Drying Oil Facility

Trouble Shooting

(a) Noisy pump

We can do calculations, but these components are not volatile, so the most likely

pump can be fixed.

(b) Problem with T-501 and the increased Dowtherm A flowrate.

Although a drop in ambient temperature might have an effect, it would be small.

As temperature drops, heat loss increases and inlet cooling water temperature

drops.

( ) ( ) ( ) ( )

p

LM

Q c m c c T

Q c U must A c T

But U will increase because the mass flow of Dowtherm has increased therefore

something in U must have decreased to compensate!

T decreases

T

LM

increases

24-17

24.16 (contd)

walls where reaction will occur. Note that there is not much DO here, so gum

formation will be slow, but only a small amount is needed for film heat transfer to

decrease.

Alternatively, the filter may not be working properly, so the gum content in

Stream 7 should be checked.

How to solve the problem?

a) If filter is a problem  recommend regular samples of Stream 7 to identify

when gum breakthrough occurs.

(c) ACO Feed problem

There are two issues:

First, the control scheme is wrong. The control valve should be using the level

control of V-501 as its signal. As it is now, the flow into V-501 will fluctuate

24.16 (contd)

A solution is to heat feed tank and also heat trace the supply line. The feed tank

may have a steam heater that no one has turned on or maybe it is malfunctioning.

The line is already insulated, but for extended periods of time this will not help.

The supply line could be retro-fitted with larger diameter pipe.

(d) Steam venting from E-506

Most probable cause is the addition of the extra pipe and elbows connecting the

exchanger to the low-pressure steam header. This extra pipe causes additional

24.17 Scale Down

The equipment that must be considered is as follows:

24-19

24.18

(a) By replacing the 1.5 in pipe with 1 in pipe, the pressure drop probably induces

cavitation in the pump. Calculations would support this. Also, having the valve

before the pump lowers the pressure, further inducing cavitation (left figure). The

figure on the right is a better design.

(b) Something is happening right after plant start up. Two possibilities come to mind. If

the heat exchanger were designed to include a fouling factor, the tubes would

probably not be fouled upon start up. Another possibility is that the catalyst

deactivates with time, but is at full activity at start up. In either case, there would be

(c) During the summer, warmer cooling water affects several units, specifically the

absorber, the distillation column, and the product cooler. The increased fuel gas rate

supports this because if the temperature in the absorber increases, absorption

equilibrium favors the vapor phase.

24.18 (contd)

(d) Additionally, the following process improvement might be a good idea. The value of

methanol in Stream 12 is about $2 million/yr. Methanol recovery should be a high

priority. Even under normal operating conditions, the absorber temperature may be

Two options for better methanol recovery might be:

24-21

24.19

(a) Fuel gas has increased in order to maintain Stream 2 at 900°F. This is probably due

to a lower HT coefficient on tube side in furnace. During temporary upset, oil would

sit inside tube and radiant furnace walls may have caused coking on the inside surface

of tubes. This means tube walls are hotter now and so this may be a problem in the

long term.

24-22

24.20

a. potential bottlenecks

flooding

reflux pump characteristics

reflux pump:

77,800/700 = 111.1 m3/h so if maximum flowrate is 149, 149/111.1 = 1.34, so 34%

E-102:

22.2

4.44

4.98

C254at hps since 4.986.155254 possible maximum

4.44

1

2

1

2

1

2

1

2

T

Q

T

Q

so 122%

T

24-23

1 = old

2 = new

38.1

10

3067.35

43.2

condensing since

11

condensing process

8.08.0

12

1211

22

11

1

2

1

2

1

2

1

2

1

2

MQ

hMMhh

hhhhhh

hh

U

M

m

Q

ii

oooi

oi

so 38%

so, flooding appears to be the limiting bottleneck

b.

24-24

24.21 Note: This is the same problem as 22.19. It may be considered a troubleshooting

problem or a multiple-unit performance problem. The problem that follows is different

but requires a similar analysis.

a.

1 = old

2 = new

use ratios

all resistance on tube side, so 8.0

mU

b.

to get system curve 2

vbaP

PPa headds

T

140

24-25

24.21 (contd)

pump-system curve plot

350

400

maximum flowrate about 47 m3/h, desired flowrate is 1.15(35) = 40.25 m3/h  no

problem

c.

d.

This is a liquid-phase reaction, so there is no effect of pressure on the reaction rate.

Also, pumps do not change liquid temperature significantly.

T

steam

24-26

24.22

a.

all resistance on tube side, so 8.0

mU

1

2

1

2

1

2

1

2

M

m

Q

s

b.

to get system curve 2

vbaP

120

T

140

90

24-27

see plot

1.315(35) = 46 m3/h

maximum flowrate is about 47 m3/h

so it is borderline, but possible

350

400